1. Field of the Invention
The present invention relates to a multi-layer circuit board used for mounting one or more semiconductor chips such as LSI's (Large Scale Integrated Circuits).
2. Description of the Related Art Including Information Disclosed Under .sctn..sctn. 1.97-1.99
LSI chips having a high integration density and operable at high speed consume a large power and require a large heat dissipation for their mounting structure. Alumina ceramics has been proposed to be used as boards for mounting such LSI chips in A. J. Blodgett, Jr. "A Multi-layer Ceramic, Multi-chip Module", IEEE Proc. of Electronics Components Conference, 1980, 283-285 and in B. T. Clark and Y. M. Hill "IBM Multichip Multilayer Ceramic Modules for LSI Chips--Design for Performance and Density", IEEE Transactions on Components, Hybrids, and Manufacturing Technology, Vol. CHMT-3, No. 1, March 1980, PP 89-93. In accordance with, however, the recent progress of LSI's, a larger heat dissipation is being required for packaging structures of the LSI's and the thermal conductivity of alumina becomes insufficient for being used in such packaging structures.
One of ceramic materials having an improved thermal conductivity is silicon carbide which is disclosed in Japanese patent application un-examined publication No. 57-180006. The silicon carbide has a resistivity of 1 to 10 ohm.multidot.cm which is still not enough to be used in the packaging structure. Berylia ceramics is another material having a large thermal conductivity. It is, however, poisonous and is not suitable to be used in an electronic device.
Recently, the use of aluminum nitride (AlN) ceramics has been proposed by Y. Kurokawa, K. Utsumi and H. Takamizawa in U.S. Pat. No. 4,650,777 which was assigned to the same assignee as the present application. AlN ceramics has characteristics generally suitable to be used in an electronic device, such as a large thermal conductivity and a high resistivity. However, Y. Kurokawa et al only suggested in the U.S. patent application to use the AlN ceramics in a semiconductor device without any concrete example of such device.
In applying the AlN ceramics to a multi-layer circuit board, the inventors of the present invention have faced some difficulties. The multi-layer circuit board interposes wiring layers between laminated layers of AlN ceramics. Since those layers are sintered at a high temperature, the wiring layers must endure the sintering process and refractory metals such as tungsten should be used therefor. However, refractory metals have a weak adhesion strength to the AlN ceramics and their coefficients of contraction are different from the AlN ceramics. Accordingly, the refractory metal wiring layers are apt to separate from the AlN ceramic layers. Such separation deteriorates the heat dissipation efficiency of the multi-layer circuit board.